Content adaptive segmented prediction

ABSTRACT

Systems and methods for content-adaptive segmented prediction mode are provided. A method includes receiving a coded picture and reconstructing a current block of the coded picture. The reconstructing includes: segmenting samples of the current block into a plurality of segments including a first segment and a second segment; predicting the first segment of the current block of the coded picture by using a first prediction mode; and predicting the second segment of the current block of the coded picture by using a second prediction mode, different from the first prediction mode.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Application No.63/073,629, filed on Sep. 2, 2020, the disclosure of which isincorporated herein by reference in its entirety.

FIELD

Embodiments of the present disclosure relate to a set of advanced videocoding technologies and, more particularly, a content-adaptive segmentedprediction mode for image and video compression.

BACKGROUND

AOMedia Video 1 (AV1) is an open video coding format designed for videotransmissions over the Internet. It was developed as a successor to VP9by the Alliance for Open Media (AOMedia), a consortium founded in 2015that includes semiconductor firms, video on demand providers, videocontent producers, software development companies, and web browservendors. Many of the components of the AV1 project were sourced fromprevious research efforts by Alliance members. Individual contributorsstarted experimental technology platforms years before: Xiph's/Mozilla'sDaala published code in 2010, Google's experimental VP9 evolutionproject VP10 was announced on Sep. 12, 2014, and Cisco's Thor waspublished on Aug. 11, 2015. Building on the codebase of VP9, AV1incorporates additional techniques, several of which were developed inthese experimental formats. The first version, version 0.1.0, of the AV1reference codec was published on Apr. 7, 2016. The Alliance announcedthe release of the AV1 bitstream specification on Mar. 28, 2018, alongwith a reference, software-based encoder and decoder. On Jun. 25, 2018,a validated version 1.0.0 of the specification was released. On Jan. 8,2019, “AV1 Bitstream & Decoding Process Specification” was released,which is a validated version 1.0.0 with Errata 1 of the specification.The AV1 bitstream specification includes a reference video codec.The“AV1 Bitstream & Decoding Process Specification” (Version 1.0.0 withErrata 1), The Alliance for Open Media (Jan. 8, 2019), is incorporatedherein in its entirety by reference.

The High Efficiency Video Coding (HEVC) standard is developed jointly bythe ITU-T Video Coding Experts Group (VCEG) and the ISO/IEC MovingPicture Experts Group (MPEG) standardization organizations. To developthe HEVC standard, these two standardization organizations work togetherin a partnership known as the Joint Collaborative Team on Video Coding(JCT-VC). The first edition of the HEVC standard was finalized inJanuary 2013, resulting in an aligned text that will be published byboth ITU-T and ISO/IEC. After that, additional work was organized toextend the standard to support several additional application scenarios,including extended-range uses with enhanced precision and color formatsupport, scalable video coding, and 3-D/stereo/multiview video coding.In ISO/IEC, the HEVC standard became MPEG-H Part 2 (ISO/IEC 23008-2) andin ITU-T it became ITU-T Recommendation H.265.

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) published theH.265/HEVC (High Efficiency Video Coding) standard in 2013 (version 1),2014 (version 2), 2015 (version 3), and 2016 (version 4). Since then,they have been studying the potential need for standardization of futurevideo coding technology which could significantly outperform HEVC incompression capability. In October 2017, they issued the Joint Call forProposals on Video Compression with Capability beyond HEVC (CfP). ByFeb. 15, 2018, 22 CfP responses on standard dynamic range (SDR), 12 CfPresponses on high dynamic range (HDR), and 12 CfP responses on 360 videocategories were submitted, respectively. In April 2018, all received CfPresponses were evaluated in the 122 MPEG/10^(th) Joint Video ExplorationTeam—Joint Video Expert Team (JVET) meeting. With careful evaluation,JVET formally launched the standardization of next-generation videocoding beyond HEVC, i.e., the so-called Versatile Video Coding (VVC).

Prior to HEVC, in December of 2001, VCEG and the Moving Picture ExpertsGroup (MPEG) ISO/IEC JTC 1/SC 29/WG 11 formed a Joint Video Team (JVT),with the charter to finalize the draft new video coding standard forformal approval submission as H.264/AVC in March 2003. H.264/AVC wasapproved by ITU-T as Recommendation H.264 and by ISO/IEC asInternational Standard 14 496-10 (MPEG-4 part 10) Advanced Video Coding(AVC).

SUMMARY

According to one or more embodiments, a method performed by at least oneprocessor is provided. The method includes receiving a coded picture,and reconstructing a current block of the coded picture. Thereconstructing includes: segmenting samples of the current block into aplurality of segments including a first segment and a second segment;predicting the first segment of the current block of the coded pictureby using a first prediction mode; and predicting the second segment ofthe current block of the coded picture by using a second predictionmode, different from the first prediction mode.

According to an embodiment, the first prediction mode is an intra blockcopy (IBC) mode, and the second prediction mode is an intra predictionmode that uses neighboring reconstructed samples to perform intraprediction.

According to an embodiment, the reconstructing the current block furtherincludes signaling the first prediction mode.

According to an embodiment, the reconstructing the current blockincludes signaling the second prediction mode.

According to an embodiment, the segmenting includes: calculating atleast one threshold value based on the samples of the current block; andsegmenting the samples of the current block based on the at least onethreshold value.

According to an embodiment, the reconstructing the current block furtherincludes segmenting samples of a reference block of the coded pictureinto a plurality of segments such as to obtain segmentation informationof the reference block, and the segmenting the samples of the currentblock includes mapping the segmentation information of the referenceblock to the current block.

According to an embodiment, the predicting the first segment of thecurrent block includes identifying, before the segmenting the samples ofthe reference block and before the segmenting the samples of the currentblock, the reference block based on a block vector, and wherein themapping includes mapping the segmentation information of the referenceblock to the current block based on the block vector.

According to an embodiment, the predicting the second segment of thecurrent block includes obtaining a prediction block that predicts thesecond segment of the current block, and the predicting the firstsegment of the current block further includes obtaining a combinedprediction block by combining, using the segmentation information, theprediction block of the current block with a segment of the referenceblock that corresponds to the first segment of the current block.

According to an embodiment, the segmentation information is asegmentation map.

According to an embodiment, the segmenting the samples of the currentblock is performed before the predicting the first segment.

According to one or more embodiments, a system is provided. The systemincludes: at least one memory configured to store computer program code;and at least one processor configured to access the computer programcode and operate as instructed by the computer program code. Thecomputer program code includes reconstructing code configured to causethe at least one processor to reconstruct a current block of a codedpicture that is received. The reconstructing code includes: currentblock segmenting code configured to cause the at least one processor tosegment samples of the current block into a plurality of segmentsincluding a first segment and a second segment; first prediction codeconfigured to cause the at least one processor to predict the firstsegment of the current block of the coded picture by using a firstprediction mode; and second prediction code configured to cause the atleast one processor to predict the second segment of the current blockof the coded picture by using a second prediction mode, different fromthe first prediction mode.

According to an embodiment, the first prediction mode is an intra blockcopy (IBC) mode, and the second prediction mode is an intra predictionmode that uses neighboring reconstructed samples to perform intraprediction.

According to an embodiment, the reconstructing code further includessignaling code that is configured to cause the at least one processor tosignal the first prediction mode.

According to an embodiment, the reconstructing code further includessignaling code that is configured to cause the at least one processor tosignal the second prediction mode.

According to an embodiment, the current block segmenting code is furtherconfigured to cause the at least one processor to: calculate at leastone threshold value based on the samples of the current block; andsegment the samples of the current block based on the at least onethreshold value.

According to an embodiment, the reconstructing code further includesreference block segmenting code that is configured to cause the at leastone processor to segment samples of a reference block of the codedpicture into a plurality of segments such as to obtain segmentationinformation of the reference block, and the current block segmentingcode is configured to cause the at least one processor to map thesegmentation information of the reference block to the current block.

According to an embodiment, the first prediction code is configured tocause the at least one processor to identify, before the samples of thereference block and the samples of the current block are segmented bythe at least one processor, the reference block based on a block vector,and the current block segmenting code is configured to cause the atleast one processor to map the segmentation information of the referenceblock to the current block based on the block vector.

According to an embodiment, the second prediction code is configured tocause the at least one processor to obtain a prediction block thatpredicts the second segment of the current block, and the firstprediction code is configured to cause the at least one processor toobtain a combined prediction block by combining, using the segmentationinformation, the prediction block of the current block with a segment ofthe reference block that corresponds to the first segment of the currentblock.

According to an embodiment, the segmentation information is asegmentation map.

According to one or more embodiments, a non-transitory computer-readablemedium storing computer instructions is provided. The computerinstructions are configured to, when executed by at least one processor,cause the at least one processor to reconstruct a current block of acoded picture that is received by: segmenting samples of the currentblock into a plurality of segments including a first segment and asecond segment; predict the first segment of the current block of thecoded picture by using a first prediction mode; and predict the secondsegment of the current block of the coded picture by using a secondprediction mode, different from the first prediction mode.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 5A a diagram illustrating a first example partition structure ofVP9.

FIG. 5B a diagram illustrating a second example partition structure ofVP9.

FIG. 5C a diagram illustrating a third example partition structure ofVP9.

FIG. 5D a diagram illustrating a fourth example partition structure ofVP9.

FIG. 6A a diagram illustrating a first example partition structure ofAV1.

FIG. 6B a diagram illustrating a second example partition structure ofAV1.

FIG. 6C a diagram illustrating a third example partition structure ofAV1.

FIG. 6D a diagram illustrating a fourth example partition structure ofAV1.

FIG. 6E a diagram illustrating a fifth example partition structure ofAV1.

FIG. 6F a diagram illustrating a sixth example partition structure ofAV1.

FIG. 6G a diagram illustrating a seventh example partition structure ofAV1.

FIG. 6H a diagram illustrating an eighth example partition structure ofAV1.

FIG. 6I a diagram illustrating a ninth example partition structure ofAV1.

FIG. 6J a diagram illustrating a tenth example partition structure ofAV1.

FIG. 7A is a diagram for demonstrating vertical binary splitting type ina multi-type tree structure.

FIG. 7B is a diagram for demonstrating horizontal binary splitting typein a multi-type tree structure.

FIG. 7C is a diagram for demonstrating vertical ternary splitting typein a multi-type tree structure.

FIG. 7D is a diagram for demonstrating horizontal ternary splitting typein a multi-type tree structure.

FIG. 8 is a diagram illustrating an example of a CTU divided intomultiple CUs with a quad tree and nested multi-type tree coding blockstructure.

FIG. 9 is a diagram illustrating eight nominal angles in AV1.

FIG. 10 is a diagram illustrating a current block and samples.

FIG. 11 is a diagram illustrating an example of intra block copycompensation.

FIG. 12 is a diagram illustrating an example of current processingblocks, restricted immediate blocks, and allowed prediction blocks withrespect to an embodiment of intra block copy prediction.

FIGS. 13A-D are illustrations of intra picture block compensation withone CTU size search range, in accordance with an embodiment.

FIG. 14 illustrates an example of intra block copy applied to videocontent.

FIG. 15 is a diagram illustrating a single block in which a plurality ofprediction modes are applied, according to embodiments of the presentdisclosure.

FIG. 16 is a diagram illustrating a process according to embodiments ofthe present disclosure.

FIG. 17 is a schematic diagram of a decoder according to an embodimentof the present disclosure.

FIG. 18 is a diagram of a computer system suitable for implementingembodiments of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure include video coding approaches,which can apply on top of multiple existing video coding standard,including but not limited to H.264/AVC, HEVC, VVC, and AV1.

In the present disclosure, the term “block” may be interpreted as aprediction block, a coding block, or a coding unit (CU). The term“block” here may also be used to refer to a transform block.

FIG. 1 illustrates a simplified block diagram of a communication system(100) according to an embodiment of the present disclosure. The system(100) may include at least two terminals (110, 120) interconnected via anetwork (150). For unidirectional transmission of data, a first terminal(110) may code video data at a local location for transmission to theother terminal (120) via the network (150). The second terminal (120)may receive the coded video data of the other terminal from the network(150), decode the coded data and display the recovered video data.Unidirectional data transmission may be common in media servingapplications and the like.

FIG. 1 illustrates a second pair of terminals (130, 140) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (130, 140) may code video data captured at a locallocation for transmission to the other terminal via the network (150).Each terminal (130, 140) also may receive the coded video datatransmitted by the other terminal, may decode the coded data, and maydisplay the recovered video data at a local display device.

In FIG. 1, the terminals (110-140) may be illustrated as servers,personal computers, and smart phones, and/or any other type of terminal.For example, the terminals (110-140) may be laptop computers, tabletcomputers, media players and/or dedicated video conferencing equipment.The network (150) represents any number of networks that convey codedvideo data among the terminals (110-140), including for example wirelineand/or wireless communication networks. The communication network (150)may exchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks, and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(150) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and decoder in astreaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

As illustrated in FIG. 2, a streaming system (200) may include a capturesubsystem (213) that can include a video source (201) and an encoder(203). The video source (201) may be, for example, a digital camera, andmay be configured to create an uncompressed video sample stream (202).The uncompressed video sample stream (202) may provide a high datavolume when compared to encoded video bitstreams, and can be processedby the encoder (203) coupled to the camera (201). The encoder (203) caninclude hardware, software, or a combination thereof to enable orimplement aspects of the disclosed subject matter as described in moredetail below. The encoded video bitstream (204) may include a lower datavolume when compared to the sample stream, and can be stored on astreaming server (205) for future use. One or more streaming clients(206) can access the streaming server (205) to retrieve video bitstreams (209) that may be copies of the encoded video bitstream (204).

In embodiments, the streaming server (205) may also function as aMedia-Aware Network Element (MANE). For example, the streaming server(205) may be configured to prune the encoded video bitstream (204) fortailoring potentially different bitstreams to one or more of thestreaming clients (206). In embodiments, a MANE may be separatelyprovided from the streaming server (205) in the streaming system (200).

The streaming clients (206) can include a video decoder (210) and adisplay (212). The video decoder (210) can, for example, decode videobitstream (209), which is an incoming copy of the encoded videobitstream (204), and create an outgoing video sample stream (211) thatcan be rendered on the display (212) or another rendering device (notdepicted). In some streaming systems, the video bitstreams (204, 209)can be encoded according to certain video coding/compression standards.Examples of such standards include, but are not limited to, ITU-TRecommendation H.265. Under development is a video coding standardinformally known as Versatile Video Coding (VVC). Embodiments of thedisclosure may be used in the context of VVC.

FIG. 3 illustrates an example functional block diagram of a videodecoder (210) that is attached to a display (212) according to anembodiment of the present disclosure.

The video decoder (210) may include a channel (312), receiver (310), abuffer memory (315), an entropy decoder/parser (320), a scaler/inversetransform unit (351), an intra prediction unit (352), a MotionCompensation Prediction unit (353), an aggregator (355), a loop filterunit (356), reference picture memory (357), and current picture memory (). In at least one embodiment, the video decoder (210) may include anintegrated circuit, a series of integrated circuits, and/or otherelectronic circuitry. The video decoder (210) may also be partially orentirely embodied in software running on one or more CPUs withassociated memories.

In this embodiment, and other embodiments, the receiver (310) mayreceive one or more coded video sequences to be decoded by the decoder(210) one coded video sequence at a time, where the decoding of eachcoded video sequence is independent from other coded video sequences.The coded video sequence may be received from the channel (312), whichmay be a hardware/software link to a storage device which stores theencoded video data. The receiver (310) may receive the encoded videodata with other data, for example, coded audio data and/or ancillarydata streams, that may be forwarded to their respective using entities(not depicted). The receiver (310) may separate the coded video sequencefrom the other data. To combat network jitter, the buffer memory (315)may be coupled in between the receiver (310) and the entropydecoder/parser (320) (“parser” henceforth). When the receiver (310) isreceiving data from a store/forward device of sufficient bandwidth andcontrollability, or from an isosynchronous network, the buffer (315) maynot be used, or can be small. For use on best effort packet networkssuch as the Internet, the buffer (315) may be required, can becomparatively large, and can be of adaptive size.

The video decoder (210) may include a parser (320) to reconstructsymbols (321) from the entropy coded video sequence. Categories of thosesymbols include, for example, information used to manage operation ofthe decoder (210), and potentially information to control a renderingdevice such as a display (212) that may be coupled to a decoder asillustrated in FIG. 2. The control information for the renderingdevice(s) may be in the form of, for example, Supplementary EnhancementInformation (SEI) messages or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (320) mayparse/entropy-decode the coded video sequence received. The coding ofthe coded video sequence can be in accordance with a video codingtechnology or standard, and can follow principles well known to a personskilled in the art, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (320) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameters corresponding to thegroup. Subgroups can include Groups of Pictures (GOPs), pictures, tiles,slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs),Prediction Units (PUs) and so forth. The parser (320) may also extractfrom the coded video sequence information such as transformcoefficients, quantizer parameter values, motion vectors, and so forth.

The parser (320) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer (315), so to create symbols(321).

Reconstruction of the symbols (321) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how they are involved, can be controlledby the subgroup control information that was parsed from the coded videosequence by the parser (320). The flow of such subgroup controlinformation between the parser (320) and the multiple units below is notdepicted for clarity.

Beyond the functional blocks already mentioned, decoder (210) can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

One unit may be the scaler/inverse transform unit (351). Thescaler/inverse transform unit (351) may receive quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (321) from the parser (320). The scaler/inversetransform unit (351) can output blocks including sample values that canbe input into the aggregator (355).

In some cases, the output samples of the scaler/inverse transform (351)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (352). In some cases, the intra pictureprediction unit (352) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture fromthe current picture memory (358). The aggregator (355), in some cases,adds, on a per sample basis, the prediction information the intraprediction unit (352) has generated to the output sample information asprovided by the scaler/inverse transform unit (351).

In other cases, the output samples of the scaler/inverse transform unit(351) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit (353) canaccess reference picture memory (357) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (321) pertaining to the block, these samples can beadded by the aggregator (355) to the output of the scaler/inversetransform unit (351) (in this case called the residual samples orresidual signal) so to generate output sample information. The addresseswithin the reference picture memory (357), from which the MotionCompensation Prediction unit (353) fetches prediction samples, can becontrolled by motion vectors. The motion vectors may be available to theMotion Compensation Prediction unit (353) in the form of symbols (321)that can have, for example, X, Y, and reference picture components.Motion compensation also can include interpolation of sample values asfetched from the reference picture memory (357) when sub-sample exactmotion vectors are in use, motion vector prediction mechanisms, and soforth.

The output samples of the aggregator (355) can be subject to variousloop filtering techniques in the loop filter unit (356). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (356) as symbols (321) from theparser (320), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (356) can be a sample stream that canbe output to a render device such as a display (212), as well as storedin the reference picture memory (357) for use in future inter-pictureprediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (320)), the current reference picturecan become part of the reference picture memory (357), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder (210) may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also, for compliance with some videocompression technologies or standards, the complexity of the coded videosequence may be within bounds as defined by the level of the videocompression technology or standard. In some cases, levels restrict themaximum picture size, maximum frame rate, maximum reconstruction samplerate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (310) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (210) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or SNR enhancementlayers, redundant slices, redundant pictures, forward error correctioncodes, and so on.

FIG. 4 illustrates an example functional block diagram of a videoencoder (203) associated with a video source (201) according to anembodiment of the present disclosure.

The video encoder (203) may include, for example, an encoder that is asource coder (430), a coding engine (432), a (local) decoder (433), areference picture memory (434), a predictor (435), a transmitter (440),an entropy coder (445), a controller (450), and a channel (460).

The encoder (203) may receive video samples from a video source (201)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (203).

The video source (201) may provide the source video sequence to be codedby the encoder (203) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source (201) may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source (203) may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can include one or more sample depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focuses on samples.

According to an embodiment, the encoder (203) may code and compress thepictures of the source video sequence into a coded video sequence (443)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofcontroller (450). The controller (450) may also control other functionalunits as described below and may be functionally coupled to these units.The coupling is not depicted for clarity. Parameters set by thecontroller (450) can include rate control related parameters (pictureskip, quantizer, lambda value of rate-distortion optimizationtechniques, . . . ), picture size, group of pictures (GOP) layout,maximum motion vector search range, and so forth. A person skilled inthe art can readily identify other functions of controller (450) as theymay pertain to video encoder (203) optimized for a certain systemdesign.

Some video encoders operate in what a person skilled in the are readilyrecognizes as a “coding loop”. As an oversimplified description, acoding loop can consist of the encoding part of the source coder (430)(responsible for creating symbols based on an input picture to be coded,and a reference picture(s)), and the (local) decoder (433) embedded inthe encoder (203) that reconstructs the symbols to create the sampledata that a (remote) decoder also would create when a compressionbetween symbols and coded video bitstream is lossless in certain videocompression technologies. That reconstructed sample stream may be inputto the reference picture memory (434). As the decoding of a symbolstream leads to bit-exact results independent of decoder location (localor remote), the reference picture memory content is also bit exactbetween a local encoder and a remote encoder. In other words, theprediction part of an encoder “sees” as reference picture samplesexactly the same sample values as a decoder would “see” when usingprediction during decoding. This fundamental principle of referencepicture synchronicity (and resulting drift, if synchronicity cannot bemaintained, for example because of channel errors) is known to a personskilled in the art.

The operation of the “local” decoder (433) can be the same as of a“remote” decoder (210), which has already been described in detail abovein conjunction with FIG. 3. However, as symbols are available anden/decoding of symbols to a coded video sequence by the entropy coder(445) and the parser (320) can be lossless, the entropy decoding partsof decoder (210), including channel (312), receiver (310), buffer (315),and parser (320) may not be fully implemented in the local decoder(433).

An observation that can be made at this point is that any decodertechnology, except the parsing/entropy decoding that is present in adecoder, may need to be present, in substantially identical functionalform in a corresponding encoder. For this reason, the disclosed subjectmatter focuses on decoder operation. The description of encodertechnologies can be abbreviated as they may be the inverse of thecomprehensively described decoder technologies. Only in certain areas amore detail description is required and provided below.

As part of its operation, the source coder (430) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (432) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (433) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (430). Operations of the coding engine (432) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (433) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture memory (434). In this manner, the encoder (203) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the codingengine (432). That is, for a new frame to be coded, the predictor (435)may search the reference picture memory (434) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(435) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (435), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (434).

The controller (450) may manage coding operations of the video coder(430), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (445). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding , variable length coding, arithmetic coding, and soforth.

The transmitter (440) may buffer the coded video sequence(s) as createdby the entropy coder (445) to prepare it for transmission via acommunication channel (460), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(440) may merge coded video data from the video coder (430) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (450) may manage operation of the encoder (203). Duringcoding, the controller (450) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as an Intra Picture (I picture), a Predictive Picture (Ppicture), or a Bi-directionally Predictive Picture (B Picture).

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh (IDR) Pictures. Aperson skilled in the art is aware of those variants of I pictures andtheir respective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (203) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (203) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional datawith the encoded video. The video coder (430) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

[Coding block partition in VP9 and AV1]

With reference to partition structures (502)-(508) of FIGS. 5A-D, VP9uses a 4-way partition tree starting from the 64×64 level down to 4×4level, with some additional restrictions for blocks 8×8. Note thatpartitions designated as R in FIG. 5D refer to recursion in that thesame partition tree is repeated at a lower scale until the lowest 4×4level is reached.

With reference to partition structures (511)-(520) of FIGS. 6A-J, AV1not only expands the partition-tree to a 10-way structure, but alsoincreases the largest size (referred to as superblock in VP9/AV1parlance) to start from 128×128. Note that this includes 4:1/1:4rectangular partitions that did not exist in VP9. The partition typeswith 3 sub-partitions as shown in FIGS. 6C-F is called a “T-type”partition. None of the rectangular partitions may be further subdivided.In addition to coding block size, coding tree depth may be defined toindicate the splitting depth from the root note. To be specific, thecoding tree depth for the root node, e.g. 128×128, is set to 0, andafter tree block is further split once, the coding tree depth isincreased by 1.

Instead of enforcing fixed transform unit sizes as in VP9, AV1 allowsluma coding blocks to be partitioned into transform units of multiplesizes that can be represented by a recursive partition going down by upto 2 levels. To incorporate AV1's extended coding block partitions,square, 2:1/1:2, and 4:1/1:4 transform sizes from 4×4 to 64×64 may besupported. For chroma blocks, only the largest possible transform unitsmay be allowed.

[Block Partitioning in HEVC]

In HEVC, a coding tree unit (CTU) may be split into coding units (CUs)by using a quadtree (QT) structure denoted as a coding tree to adapt tovarious local characteristics. The decision on whether to code a picturearea using inter-picture (temporal) or intra-picture (spatial)prediction may be made at the CU level. Each CU can be further splitinto one, two, or four prediction units (PUs) according to the PUsplitting type. Inside one PU, the same prediction process may beapplied and the relevant information is transmitted to the decoder on aPU basis. After obtaining the residual block by applying the predictionprocess based on the PU splitting type, a CU can be partitioned intotransform units (TUs) according to another quad tree structure like thecoding tree for the CU. One of key features of the HEVC structure isthat it has the multiple partition concepts including CU, PU, and TU. InHEVC, a CU or a TU can only have a square shape, while a PU may have asquare or rectangular shape for an inter predicted block. In HEVC, onecoding block may be further split into four square sub-blocks, andtransform is performed on each sub-block (i.e. TU). Each TU can befurther split recursively (using quadtree split) into smaller TUs, whichis called a Residual Quad-Tree (RQT).

At picture boundary, HEVC employs implicit quad-tree split so that ablock will keep quad-tree splitting until the size fits the pictureboundary.

[Quadtree with Nested Multi-Type Tree Coding Block Structure in VVC]

In VVC, a quadtree with nested multi-type tree using binary and ternarysplits segmentation structure replaces the concepts of multiplepartition unit types. That is, VVC does not include the separation ofthe CU, PU, and TU concepts except as needed for CUs that have a sizetoo large for the maximum transform length, and supports moreflexibility for CU partition shapes. In the coding tree structure, a CUcan have either a square or rectangular shape. A coding tree unit (CTU)is first partitioned by a quaternary tree (a.k.a. quad tree) structure.Then, the quaternary tree leaf nodes can be further partitioned by amulti-type tree structure. As shown in diagrams (532), (534), (536), and(538) of FIGS. 7A-D, there are four splitting types in multi-type treestructure: vertical binary splitting (SPLIT_BT_VER) as illustrated inFIG. 7A, horizontal binary splitting (SPLIT_BT_HOR) as illustrated inFIG. 7B, vertical ternary splitting (SPLIT_TT_VER) as illustrated inFIG. 7C, and horizontal ternary splitting (SPLIT_TT_HOR) as illustratedin FIG. 7D. The multi-type tree leaf nodes may be called coding units(CUs), and unless the CU is too large for the maximum transform length,this segmentation may be used for prediction and transform processingwithout any further partitioning. This means that, in most cases, theCU, PU and TU have the same block size in the quadtree with nestedmulti-type tree coding block structure. The exception occurs whenmaximum supported transform length is smaller than the width or heightof the color component of the CU. One example of block partition for oneCTU is shown in FIG. 8. FIG. 8 shows a CTU (540) divided into multipleCUs with a quadtree and nested multi-type tree coding block structure,where the bold line edges represent quadtree partitioning and the brokenline edges represent multi-type tree partitioning. The quadtree withnested multi-type tree partition provides a content-adaptive coding treestructure comprised of CUs.

In VVC, the maximum supported luma transform size is 64×64 and themaximum supported chroma transform size is 32×32. When the width orheight of the CB is larger than the maximum transform width or height,the CB may be automatically split in the horizontal and/or verticaldirection to meet the transform size restriction in that direction.

In VTM7, the coding tree scheme supports the ability for the luma andchroma to have a separate block tree structure. For P and B slices, theluma and chroma CTBs in one CTU may have to share the same coding treestructure. However, for I slices, the luma and chroma can have separateblock tree structures. When separate block tree mode is applied, lumaCTB is partitioned into CUs by one coding tree structure, and the chromaCTBs are partitioned into chroma CUs by another coding tree structure.This means that a CU in an I slice may consist of a coding block of theluma component or coding blocks of two chroma components, and a CU in aP or B slice may consist of coding blocks of all three colour componentsunless the video is monochrome.

[Directional Intra Prediction in AV1]

VP9 supports eight directional modes corresponding to angles from 45 to207 degrees. To exploit more varieties of spatial redundancy indirectional textures, in AV1, directional intra modes are extended to anangle set with finer granularity. The original eight angles are slightlychanged and made as nominal angles, and these 8 nominal angles are namedas V_PRED (542), H_PRED (543), D45_PRED (544), D135_PRED (545),D113_PRED (546), D157_PRED (547), D203_PRED (548), and D67_PRED (549),which are illustrated in FIG. 9 with respect to a current block (541).For each nominal angle, there are seven finer angles, so AV1 has 56directional angles in total. The prediction angle is presented by anominal intra angle plus an angle delta, which is −3˜3 multiples of thestep size of 3 degrees. To implement directional prediction modes in AV1via a generic way, all the 56 directional intra prediction mode in AV1are implemented with a unified directional predictor that projects eachpixel to a reference sub-pixel location and interpolates the referencepixel by a 2-tap bilinear filter.

[Non-Directional Smooth Intra Predictors in AV1]

In AV1, there are five non-directional smooth intra prediction modes,which are DC, PAETH, SMOOTH, SMOOTH_V, and SMOOTH_H. For DC prediction,the average of left and above neighboring samples is used as thepredictor of the block to be predicted. For PAETH predictor, top, left,and top-left reference samples are firstly fetched, and then the valuewhich is closest to (top+left−topleft) is set as the predictor for thepixel to be predicted. FIG. 10 illustrates the positions of a top sample(554), a left sample (556), and a top-left sample (558) for a currentpixel (552) in a current block (550). For SMOOTH, SMOOTH_V, and SMOOTH_Hmodes, the current block (550) is predicted using quadraticinterpolation in vertical or horizontal directions, or the average ofboth directions.

[Chroma Predicted from Luma]

For chroma component, besides 56 directional modes and 5 non-directionalmode, chroma from luma (CfL) is a chroma-only intra prediction mode,which models chroma pixels as a linear function of coincidentreconstructed luma pixels. The CfL prediction may be expressed as shownbelow in Equation 1:

CfL(a)=a×L _(AC) +DC  (Equation 1)

wherein L_(AC) denotes the AC contribution of the luma component, adenotes the parameter of the linear model, and DC denotes the DCcontribution of the chroma component. To be specific, the reconstructedluma pixels are subsampled into the chroma resolution, and then theaverage value is subtracted to form the AC contribution. To approximatethe chroma AC component from the AC contribution, instead of requiringthe decoder to calculate the scaling parameters as in some backgroundart, AV1 CfL determines the parameter a based on the original chromapixels and signals them in the bitstream. This reduces decodercomplexity and yields more precise predictions. As for the DCcontribution of the chroma component, it may be computed using intra DCmode, which is sufficient for most chroma content and has mature fastimplementations.

For the signaling of chroma intra prediction modes, eight nominaldirectional modes, 5 non-directional modes, and CfL mode may be firstlysignaled. The context for signaling these modes may be dependent on thecorresponding luma mode of the top-left position of a current block.Then, if the current chroma mode is a directional mode, one additionalflag may be signaled to indicate the delta angle to the nominal angle.

[Intra Block Copy]

Block based compensation from a different picture may be referred to asmotion compensation. Similarly, a block compensation can also be donefrom a previously reconstructed area within the same picture. This maybe referred to as intra picture block compensation, current picturereferencing (CPR), or intra block copy (IBC). A displacement vector thatindicates the offset between the current block and the reference blockmay be referred as the block vector (BV). Different from a motion vectorin motion compensation, which can be at any value (positive or negative,at either x or y direction), a block vector has a few constraints suchthat the pointed reference block is ensured to be available and alreadyreconstructed. Also, for parallel processing consideration, somereference area that is a tile boundary or a wavefront ladder shapeboundary may also be excluded.

The coding of a block vector may be either explicit or implicit. In theexplicit mode (referred to as AMVP mode in inter coding), the differencebetween a block vector and its predictor may be signaled; in theimplicit mode, the block vector may recovered purely from its predictor,in a similar way as a motion vector in merge mode. The resolution of ablock vector, in some implementations, is restricted to integerpositions; in other systems, it may be allowed to point to fractionalpositions.

The use of intra block copy at block level can be signaled using a blocklevel flag (e.g. an IBC flag). In one embodiment, this flag is signaledwhen the current block is not coded in merge mode. Or, it can besignaled by a reference index approach. This may be done by treating thecurrent decoded picture as a reference picture. In HEVC SCC, such areference picture may be put in the last position of the list. Thisspecial reference picture may also be managed together with othertemporal reference pictures in the decoded picture buffer (DPB).

There are also some variations for intra block copy, such as treatingthe intra block copy as a third mode, which is different from eitherintra or inter prediction mode. By doing this, the block vectorprediction in merge mode and AMVP mode are separated from regular intermode. For example, a separate merge candidate list is defined for intrablock copy mode, where all the entries in the list are block vectors.Similarly, the block vector prediction list in intra block copy AMVPmode only consists of block vectors. A general rule applied to bothlists is that they may follow the same logic as inter merge candidatelist or AMVP predictor list in terms of candidate derivation process.For example, the five spatial neighboring locations in HEVC or VVC intermerge mode are accessed for intra block copy to derive its own mergecandidate list. An example of intra block copy is shown in FIG. 11,which illustrates a current picture (560) in which a current block (562)is predicted based on a reference block (564) whose position isindicated by a block vector (566).

IBC (also called IntraBC) is very effective for screen content coding,but it also brings a lot of difficulties to hardware design. Tofacilitate the hardware design, the following modifications may beadopted in AV1.

-   -   Modification 1: When IBC is allowed, the loop filters are        disabled, which are de-blocking filter, the CDEF (Constrained        Directional Enhancement Filter), and the Loop Restoration. By        doing this, picture buffer of reconstructed samples can be        shared between IBC and inter prediction.    -   Modification 2: To facilitate parallel decoding, the prediction        cannot exceed the restricted areas. For one super block, if the        coordinate of its top-left position is (x0, y0), the prediction        at position (x, y) can be accessed by IBC, if y<y0 and        x<x0+2*(y0−y)3.

To allow hardware writing back delay, immediate reconstructed areas maynot be accessed by IBC prediction. The restricted immediatereconstructed area can be 1˜n super blocks. So on top of modification 2,if the coordinate of one super block's top-left position is (x0, y0),the prediction at position (x, y) can be accessed by IBC, if y<y0 andx<x0+2*(y0−y)−D, where D denotes the restricted immediate reconstructedarea. When D is one super block, the prediction area may be as shown inFIG. 12. In FIG. 12, a plurality of current processing blocks (572) areshown with diagonal stripes, a plurality of restricted immediate blocks(574) are shown with cross-hatching, and a plurality of allowedprediction blocks (576) are shown with a dark pattern.

In VVC, the search range of IBC mode may be constrained to be within thecurrent CTU. The effective memory requirement to store reference samplesfor IBC mode may be 1 CTU size of samples. Considering the existingreference sample memory to store reconstructed samples in current 64×64region, three more 64×64 sized reference sample memory may be required.Based on this fact, a method of embodiments of the present disclosuremay extend the effective search range of the IBC mode to some part ofthe left CTU while the total memory requirement for storing referencepixels are kept unchanged (1 CTU size, 4 64×64 reference sample memoryin total). An example of such memory reuse mechanism is shown in FIGS.13A-D, where the diagonally striped block is a current coding region,samples in the dotted patterned boxes are coded samples, and the crossedout regions (marked with “X”) are not available for reference as theyare replaced in the reference sample memory by the coding regions incurrent CTU.

For example, in FIG. 13A, reference sample (612 a), marked with an X, isunavailable for current sample (611). Similarly, in FIG. 13B, referencesamples (622 a) and (622 b) are unavailable for current sample (621). InFIG. 13C, reference samples (632 a), (632 b), and (632 c) areunavailable for current sample 631, and in FIG. 13D, reference samples(642 a), (642 b), (642 c), and (642 d) are unavailable for currentsample (641).

[Problems with Coding Modes of Comparative Art]

IBC as well as other coding modes may assume single texture patternwithin one block. However, in many typical video contents, objects haveocclusions to each other. For example, texts and logos that do not moveare floating on top of the main video content that have completelydifferent texture pattern or motion. For example, as shown in the videoframe (700) illustrated in FIG. 14, it can be seen that there areexamples of two matching characters “o” (702) and “E” (704). However,these matching characters are located on top of different backgroundsand IBC, which assumes all samples share the same block vector, andtherefore cannot capture both texts and backgrounds efficiently.

[Example Aspects of Embodiments of the Present Disclosure]

Embodiments of the present disclosure may be used separately or combinedin any order. Further, each embodiment (e.g. methods, encoders, anddecoders) may be implemented by processing circuitry (e.g. one or moreprocessors or one or more integrated circuits). In one example, the oneor more processors execute a program that is stored in a non-transitorycomputer-readable medium.

Embodiments of the present disclosure may incorporate any number ofaspects as described above. Embodiments of the present disclosure mayalso incorporate one or more of the aspects described below, and solvethe problems discussed above and/or other problems.

A. First Aspect

According to embodiments instead of applying one single prediction modefor a block, a plurality of prediction modes can be applied for a singleblock, and a segmentation process may be performed to divide the samplesin the single block into different segments, and each segment may beassociated with one of the selected prediction modes. Then, for samplesthat belong to a first segment, the associated first prediction mode isused to generate the prediction samples for the first segment; forsamples that belong to a second segment, the associated secondprediction mode is used to generate the prediction samples for thesecond segment, and so on. FIG. 15 illustrates an example of suchprocess, where samples of a current block (722) are classified(segmented) into a first segment (A) and a second segment (B). Samplesof the first segment (A) may be predicted by applying an IBC mode usinga block vector (726) to fetch a prediction block (724), and samples ofthe second segment (B) may be predicted by applying a normal intraprediction mode using neighboring reconstructed samples to generateprediction values.

According to an embodiment, a plurality of prediction modes can besignaled for a block (e.g. the current block (722)). In one example, theplurality of prediction modes include an IBC prediction mode (includinga block vector) and an intra prediction mode (including an intraprediction mode or direction) that uses neighboring reconstructedsamples to perform the intra prediction.

According to an embodiment, IBC is applied together with one or moredefault intra prediction modes for a single block (e.g. the currentblock (722)), and only mode information related to IBC (e.g. blockvector) is signaled. For samples within the single block, the IBC modeis applied for some samples, and the one or more default intraprediction modes are applied for the remaining samples. The defaultintra prediction modes include, but are not limited to, DC, Planar,SMOOTH, SMOOTH_H, SMOOTH_V, Paeth, and Plane modes.

According to an embodiment, IBC is applied together with one or moredefault intra prediction modes for a single block (e.g. the currentblock (722)), and the mode information related to IBC (e.g. blockvector) is inferred. For samples within the single block, the IBC modeis applied for some samples, and the one or more default intraprediction modes are applied for the remaining samples. The inferred IBCinformation (block vector) can be derived (e.g. by a decoder) from ablock vector predictor list, such as those used for generating a mergelist. If more than one possible block vector candidate exists, an indexvalue may be signaled for the selection of a block vector from the blockvector predictor list. For example, the index value may be received bythe decoder from the encoder. Otherwise, a default selection can be madewithout the encoder sending the index and the decoder receiving theindex. In this case, for example, the first block vector candidate inthe predictor list may be assumed (e.g. by the decoder) to be used. Thedefault intra prediction modes include, but are not limited to, DC,Planar, SMOOTH, SMOOTH_H, SMOOTH_V, Paeth, and Plane modes.

Embodiments (e.g. decoders) may perform the segmentation process indifferent ways. According to embodiments, the segmentation process maybe performed on the current block (722). In one example, a thresholdvalue of the samples within the single current block (722) is firstcalculated. According to the threshold, samples are classified intodifferent segments by comparing their value with the threshold value.The threshold value includes, but is not limited to, the mean, medianvalue, or other values that is derived from the mean or median value. Inanother example, a histogram of the distribution of values of thesamples is calculated. According to the histogram, one or more thresholdvalues on the sample counts are derived, and samples are classified intodifferent segments by comparing their sample count in the histogram andthe threshold values. In another example, a convolutional neural networkis applied using the samples of the current block (722) as an input, andthe output of the convolutional neural network is a segment index foreach sample. In another example, edge detection methods may be appliedto the block. Segmentation may be done according to possible edgeboundaries.

According to one or more embodiments, with reference to FIG. 16, thesegmentation is first applied on a reference block (730), then thesegmentation information is further mapped to a current block (740) toderive the segmentation of the samples of the current block (740). Inone example, a block vector is used to identify the reference block(730) in neighboring reconstructed areas, segmentation is applied on thereference block (730), and then the segmentation information is mappedto the current block (740) using the block vector. With reference toFIG. 16, the reference block (730) for the current block (740) isderived using a block vector within the same picture. Then, asegmentation process is applied on the reference block (730), and thereference block (730) is divided into, for example, multiple parts (e.g.a first segment (732) and a second segment (734)). In the example shownin FIG. 16, the first segment (732) includes areas outside an image of abird, and the second segment (734) includes the image of the bird. Inthe segmentation process, a segmentation map (736) is obtained thatindicates the segment index for each sample. With reference to FIG. 16,the black portion of the segmentation map (736) corresponds to the firstsegment (732), and the white portion of the segmentation map (736)corresponds to the second segment (734). Then, the segmentation map(736) is mapped to the current block (740) using the block vector toderive the segmentation information of the current block (740). Based onthe segmentation information, the current block (740) is segmented intomultiple segments (e.g. two segments corresponding to the first segment(732) and the second segment (734)). For example, a first segment of thecurrent block (740) includes areas outside an image of a bird, and asecond segment of the current block (740) includes the image of thebird. Then, a conventional prediction process is applied for the currentblock (740) to derive a conventional prediction block (750). Forexample, the conventional prediction process may applied for the firstsegment of the current block (740), which includes areas outside theimage of the bird, and not the second segment of the current block(740). Finally, the conventional prediction block (750) and the secondsegment (734), from the reference block (730), are combined using thesegmentation map (736) to derive a combined prediction block (760).

For each segment, prediction samples may be generated within the segmentboundary. After predicting samples of each possible segment, predictedsegments may be merged together to form a final predictor of the currentblock (740). This prediction block, together with possible decodedresidue block signal, can form the reconstructed block (before any loopfiltering) by adding the two together.

According to embodiments, the identifying the reference block (730), thepredicting using the second segment (734) of the reference block (730),and the combining of the second segment (734) with the conventionalprediction block (750) may be considered as a part of a prediction modeother than the conventional prediction process used to obtain thecombined prediction block (760).

B. Second Aspect

According to the examples described above with respect to the firstaspect, block vector of intra block copy mode and intra predictiondirection (or non-directional mode option) may need to be specified forthe segmented prediction mode. Non-limiting example processes of theselection that may be performed (e.g. by a decoder) are described below.

In one embodiment, a block vector of IBC mode is signaled to indicatethe reference block location. The signaling can be based on vectorprediction and a coded difference. The coded difference may be adifference between the block vector and its predictor, and may bereceived by the decoder from the encoder.

In another embodiment, a block vector candidate list is obtained, andone candidate is chosen from the list by signaling the index of an entryin the list. The chosen candidate is used as the block vector without adifference being coded.

In another embodiment, a block vector candidate list is obtained, andone candidate is chosen from the list by selecting a default entryposition in the list. For example, a decoder may choose the first entryin the list as the default entry position. In this case, no index mayneed to be signaled. The chosen candidate is used as the block vectorwithout a difference being coded.

In another embodiment, an intra mode is signaled to indicate the intraprediction method for one of the segments. The signaling can be based ona separate set of intra prediction modes. In one example, regular intraprediction may have M prediction modes while the separate set of intraprediction modes may be N modes. N may not be equal to M. A MostProbable Mode (MPM) list may be obtained to predict the selected intramode. In one example, the N intra prediction modes can be a subset ofthe full set of M regular intra prediction modes.

In another embodiment, an intra prediction mode candidate list isobtained, and one candidate is chosen from the list by signaling anindex of an entry in the list. The chosen candidate is used as the intraprediction mode without a difference being coded.

In another embodiment, an intra prediction mode candidate list isobtained, and one candidate is chosen from the list by selecting adefault entry position in the list. For example, a decoder may choosethe first entry in the list as the default entry position. In this case,no index may need to be signaled. The chosen candidate is used as theintra prediction mode without a difference being coded.

According to embodiments, at least one processor and memory storingcomputer program instructions may be provided. The computer programinstructions, when executed by the at least one processor, may implementan encoder or a decoder and may perform any number of the functionsdescribed in the present disclosure. For example, with reference to FIG.17, the at least one processor may implement a decoder (800). Thecomputer program instructions may include, for example, reconstructingcode (810) that is configured to cause the at least one processor toreconstruct a current block of a coded picture that is received (e.g.from an encoder). The reconstructing code (810) may include, forexample, signaling or inferring code (820), segmenting code (830), firstprediction code (840), and/or second prediction code (850).

The signaling or inferring code (820) may be configured to cause the atleast one processor to signal values of syntax elements (e.g. flags,indexes, etc.), in accordance with embodiments of the presentdisclosure, which may be received by the decoder 800 from an encoder orotherwise obtained. Alternatively or additionally, signaling orinferring code (820) may be configured to cause the at least oneprocessor to infer information (e.g. default intra prediction modesand/or mode information related to IBC), in accordance with embodimentsof the present disclosure.

The segmenting code (830) may include current block segmenting code thatis configured to cause the at least one processor to segment samples ofthe current block into a plurality of segments including a first segmentand a second segment, in accordance with embodiments of the presentdisclosure. For example, the current block segmenting code may beconfigured to cause the at least one processor to calculate at least onethreshold value based on the samples of the current block, and segmentthe samples of the current block based on the at least one thresholdvalue. In such case and other cases, the segmenting of the samples ofthe current block may be performed before applying a first predictionmode. Alternatively, with reference to descriptions of FIG. 16, thecurrent block segmenting code may be configured to cause the at leastone processor to segment the samples of the current block by mappingsegmentation information (e.g. a segmentation map) of a reference blockthat is obtained to the current block. In such case, the segmenting code(830) may further include reference block segmenting code that isconfigured to cause the at least one processor to segment samples of thereference block of the coded picture into a plurality of segments suchas to obtain the segmentation information of the reference block. Insuch case and other cases, the segmenting of samples may be performedconcurrently, at least in part, with the applying of the firstprediction mode.

The first prediction code (840) may be configured to cause the at leastone processor to apply the first prediction mode for prediction of thefirst segment of the current block of the coded picture, in accordancewith embodiments of the present disclosure. According to embodiments,the first prediction mode may be the IBC mode. According to embodimentswith reference to FIG. 16, the first prediction code (840) may beconfigured to cause the at least one processor to identify, before thesegmenting the samples of the reference block and before the segmentingthe samples of the current block, the reference block based on a blockvector. In such case, the first prediction code (840) may be configuredto cause the at least one processor to obtain a combined predictionblock by combining, using the segmentation information, a predictionblock of the current block with a segment of the reference block thatcorresponds to the first segment of the current block.

The second prediction code (850) may be configured to cause the at leastone processor to apply a second prediction mode, different from thefirst prediction mode, for prediction of the second segment of thecurrent block of the coded picture. According to embodiments, the secondprediction mode may an intra prediction mode that uses neighboringreconstructed samples to perform intra prediction. According toembodiments with reference to FIG. 16, the second prediction code (850)may be configured to cause the at least one processor to obtain theprediction block that predicts the second segment of the current block,wherein the prediction block is used to obtain the combined predictionblock.

According to embodiments, the encoder-side processes corresponding tothe above processes may be implemented by encoding code for encoding apicture as would be understood by a person of ordinary skill in the art,based on the above descriptions.

The techniques of embodiments of the present disclosure described above,can be implemented as computer software using computer-readableinstructions and physically stored in one or more computer-readablemedia. For example, FIG. 18 shows a computer system (900) suitable forimplementing embodiments of the disclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 18 for computer system (900) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (900).

Computer system (900) may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (901), mouse (902), trackpad (903), touchscreen (910), data-glove , joystick (905), microphone (906), scanner(907), and camera (908).

Computer system (900) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (910), data-glove, or joystick (905), but there can also betactile feedback devices that do not serve as input devices). Forexample, such devices may be audio output devices (such as: speakers(909), headphones (not depicted)), visual output devices (such asscreens (910) to include CRT screens, LCD screens, plasma screens, OLEDscreens, each with or without touch-screen input capability, each withor without tactile feedback capability—some of which may be capable tooutput two dimensional visual output or more than three dimensionaloutput through means such as stereographic output; virtual-realityglasses (not depicted), holographic displays and smoke tanks (notdepicted)), and printers (not depicted).

Computer system (900) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(920) with CD/DVD or the like media (921), thumb-drive (922), removablehard drive or solid state drive (923), legacy magnetic media such astape and floppy disc (not depicted), specialized ROM/ASIC/PLD baseddevices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (900) can also include interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (949) (such as, for example USB ports of thecomputer system (900); others are commonly integrated into the core ofthe computer system 900 by attachment to a system bus as described below(for example Ethernet interface into a PC computer system or cellularnetwork interface into a smartphone computer system). Using any of thesenetworks, computer system (900) can communicate with other entities.Such communication can be uni-directional, receive only (for example,broadcast TV), uni-directional send-only (for example CANbus to certainCANbus devices), or bi-directional, for example to other computersystems using local or wide area digital networks. Such communicationcan include communication to a cloud computing environment (955).Certain protocols and protocol stacks can be used on each of thosenetworks and network interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces (954) can be attached to a core (940) ofthe computer system (900).

The core (940) can include one or more Central Processing Units (CPU)(941), Graphics Processing Units (GPU) (942), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(943), hardware accelerators (944) for certain tasks, and so forth.These devices, along with Read-only memory (ROM) (945), Random-accessmemory (946), internal mass storage such as internal non-user accessiblehard drives, SSDs, and the like (947), may be connected through a systembus (948). In some computer systems, the system bus (948) can beaccessible in the form of one or more physical plugs to enableextensions by additional CPUs, GPU, and the like. The peripheral devicescan be attached either directly to the core's system bus (948), orthrough a peripheral bus (949). Architectures for a peripheral businclude PCI, USB, and the like. A graphics adapter (950) may be includedin the core (940).

CPUs (941), GPUs (942), FPGAs (943), and accelerators (944) can executecertain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(945) or RAM (946). Transitional data can be also be stored in RAM(946), whereas permanent data can be stored for example, in the internalmass storage (947). Fast storage and retrieve to any of the memorydevices can be enabled through the use of cache memory, that can beclosely associated with one or more CPU (941), GPU (942), mass storage(947), ROM (945), RAM (946), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (900), and specifically the core (940) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (940) that are of non-transitorynature, such as core-internal mass storage (947) or ROM (945). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (940). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(940) and specifically the processors therein (including CPU, GPU, FPGA,and the like) to execute particular processes or particular parts ofparticular processes described herein, including defining datastructures stored in RAM (946) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (944)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several non-limiting exampleembodiments, there are alterations, permutations, and various substituteequivalents, which fall within the scope of the disclosure. It will thusbe appreciated that those skilled in the art will be able to devisenumerous systems and methods which, although not explicitly shown ordescribed herein, embody the principles of the disclosure and are thuswithin the spirit and scope thereof.

What is claimed is:
 1. A method performed by at least one processor, themethod comprising: receiving a coded picture; and reconstructing acurrent block of the coded picture, the reconstructing comprising:segmenting samples of the current block into a plurality of segmentsincluding a first segment and a second segment; predicting the firstsegment of the current block of the coded picture by using a firstprediction mode; and predicting the second segment of the current blockof the coded picture by using a second prediction mode, different fromthe first prediction mode.
 2. The method of claim 1, wherein the firstprediction mode is an intra block copy (IBC) mode, and the secondprediction mode is an intra prediction mode that uses neighboringreconstructed samples to perform intra prediction.
 3. The method ofclaim 2, wherein the reconstructing the current block further comprisessignaling the first prediction mode.
 4. The method of claim 2, whereinthe reconstructing the current block comprises signaling the secondprediction mode.
 5. The method of claim 1, wherein the segmentingcomprises: calculating at least one threshold value based on the samplesof the current block; and segmenting the samples of the current blockbased on the at least one threshold value.
 6. The method of claim 1,wherein the reconstructing the current block further comprisessegmenting samples of a reference block of the coded picture into aplurality of segments such as to obtain segmentation information of thereference block, and the segmenting the samples of the current blockcomprises mapping the segmentation information of the reference block tothe current block.
 7. The method of claim 6, wherein the predicting thefirst segment of the current block comprises identifying, before thesegmenting the samples of the reference block and before the segmentingthe samples of the current block, the reference block based on a blockvector, and wherein the mapping comprises mapping the segmentationinformation of the reference block to the current block based on theblock vector.
 8. The method of claim 7, wherein the predicting thesecond segment of the current block comprises obtaining a predictionblock that predicts the second segment of the current block, and thepredicting the first segment of the current block further comprisesobtaining a combined prediction block by combining, using thesegmentation information, the prediction block of the current block witha segment of the reference block that corresponds to the first segmentof the current block.
 9. The method of claim 8, wherein the segmentationinformation is a segmentation map.
 10. The method of claim 1, whereinthe segmenting the samples of the current block is performed before thepredicting the first segment.
 11. A system comprising: at least onememory configured to store computer program code; and at least oneprocessor configured to access the computer program code and operate asinstructed by the computer program code, the computer program codecomprising: reconstructing code configured to cause the at least oneprocessor to reconstruct a current block of a coded picture that isreceived, the reconstructing code comprising: current block segmentingcode configured to cause the at least one processor to segment samplesof the current block into a plurality of segments including a firstsegment and a second segment; first prediction code configured to causethe at least one processor to predict the first segment of the currentblock of the coded picture by using a first prediction mode; and secondprediction code configured to cause the at least one processor topredict the second segment of the current block of the coded picture byusing a second prediction mode, different from the first predictionmode.
 12. The system of claim 11, wherein the first prediction mode isan intra block copy (IBC) mode, and the second prediction mode is anintra prediction mode that uses neighboring reconstructed samples toperform intra prediction.
 13. The system of claim 12, wherein thereconstructing code further comprises signaling code that is configuredto cause the at least one processor to signal the first prediction mode.14. The system of claim 12, wherein the reconstructing code furthercomprises signaling code that is configured to cause the at least oneprocessor to signal the second prediction mode.
 15. The system of claim11, wherein the current block segmenting code is further configured tocause the at least one processor to: calculate at least one thresholdvalue based on the samples of the current block; and segment the samplesof the current block based on the at least one threshold value.
 16. Thesystem of claim 11, wherein the reconstructing code further comprisesreference block segmenting code that is configured to cause the at leastone processor to segment samples of a reference block of the codedpicture into a plurality of segments such as to obtain segmentationinformation of the reference block, and the current block segmentingcode is configured to cause the at least one processor to map thesegmentation information of the reference block to the current block.17. The system of claim 16, wherein the first prediction code isconfigured to cause the at least one processor to identify, before thesamples of the reference block and the samples of the current block aresegmented by the at least one processor, the reference block based on ablock vector, and the current block segmenting code is configured tocause the at least one processor to map the segmentation information ofthe reference block to the current block based on the block vector. 18.The system of claim 17, wherein the second prediction code is configuredto cause the at least one processor to obtain a prediction block thatpredicts the second segment of the current block, and the firstprediction code is configured to cause the at least one processor toobtain a combined prediction block by combining, using the segmentationinformation, the prediction block of the current block with a segment ofthe reference block that corresponds to the first segment of the currentblock.
 19. The system of claim 18, wherein the segmentation informationis a segmentation map.
 20. A non-transitory computer-readable mediumstoring computer instructions that are configured to, when executed byat least one processor, cause the at least one processor to: reconstructa current block of a coded picture that is received by: segmentingsamples of the current block into a plurality of segments including afirst segment and a second segment; predict the first segment of thecurrent block of the coded picture by using a first prediction mode; andpredict the second segment of the current block of the coded picture byusing a second prediction mode, different from the first predictionmode.